Selective hydrocracking before and after reforming

ABSTRACT

PROCESSING NAPHTHA TO PRODUCE SIGNIFICANT YIELDS OF LPG AND AN AROMATIC RICH CONCENTRATE IS DESCRIBED BY THE SELECTIVE HYDROCRACKING OF NORMAL PARAFFINS TO LPG MATERIAL WITH A SMALL PORE CRYSTALLINE ZEOLITE HYDROCRACKING CATALYST BEFORE AND AFTER PLATINUM REFORMING.   D R A W I N G

April 23, 1974 J. MAZIUK 3,306,443

SELECTIVE HYDROCRACKING BEFORE AND AFTER REFORMING Filed May 26, 1972 5m b) w w 1159 Q 0 I l no 0: \Kg l v v L v N "a W n l Nophfho Feed UnitedStates Patent US. Cl. 208-60 8 Claims ABSTRACT OF THE DISCLOSUREProcessing naphtha to produce significant yields of LPG and an aromaticrich concentrate is described by the selective hydrocracking of normalparafiins to LPG material with a small pore crystalline zeolitehydrocracking catalyst before and after platinum reforming.

BACKGROUND OF THE INVENTION Reforming of hydrocarbons is a widely usedprocess in petroleum technology for upgrading hydrocarbon fractions suchas naphthas, gasolines and kerosines to improve the anti-knockcharacteristics thereof. Hydrocarbon fractions suitable for upgrading byreforming are composed of normal and branched parafiins, naphthenichydrocarbons and even some aromatic hydrocarbons. During reforming amultitude of reactions take place including dehydrogenation,isomerization, dehydrocyclization, hydrocracking, and combinationsthereof to yield a product of increased aromatics content and branchedchain hydrocarbons. Thus in reforming it is desired to dehydrogenate thenaphthenic hydrocarbons to produce aromatics, cyclize straight chainparaffins to form naphthenes, to convert C ring compounds to C ringcompounds which are dehydrogenated to for maromatics, isomerize normaland branched paraffin hydrocarbons to yield higher octane branched chainhydrocarbons and effect a controlled hydrocracking of hydrocarbonconstituents which are of undesired octane characteristics.

Normal and slightly branched paraflin hydrocarbons found in the abovehydrocarbon fractions are generally of low octane rating. Highlybranched-chain parafiin hydrocarbons, on the other hand, arecharacteristic of higher octane ratings. Therefore, one object ofreforming is to effect isomerization of the normal and slightly branchedchain parafiins to higher octane products by any one of theaforementioned reactions. The production of aromatics during reformingis accomplished by one or more of the above identified reactions leadingto the production of naphthenes which are then dehydrogenated toaromatics such as benzene, toluene and xylene. One method for producingaromatics involves the isomerization of alkyl cyclopentanes to formcyclohexanes which thereafter are dehydrogenated to aromatics.

Ever since the concept of catalytic reforming was developed andcommercially adopted, the refiner has been concerned with improving uponthe selectivity of the product obtained and thus has strived to reduceyields of carbon and normally gaseous product materials since suchmaterials represent a loss in desired liquid product. Thus smallimprovement in product selectivity has been gained with difficulty sincethere is a limit to the quantity of normally liquid constituents ofdesired octane rating that can be produced from a given charge.Consequently increases in product selectivity are viewed withconsiderable interest particularly if the selectivity increases can beassociated with products of economic interest to the refiner. It hasbeen found that the selectivity of a particular product slate orcomposition can be considerably enhanced by following the concepts andsequence of steps comprising this invention.

THE INVENTION This invention relates to a method and combination ofprocessing steps for effecting a selective conversion and arearrangement of petroleum hydrocarbon constituents to form aromaticenriched products and improve yields of LPG materials. In one aspect thepresent invention is concerned with one or more methods for selectivelyconducting chemical reactions with an arrangement of catalyticcompositions possessing selective reaction properties with respect todifferent hydrocarbon components existing in the naphtha boiling rangematerial. In yet another aspect the present invention relates toeffecting a selective catalytic conversion of hydrocarbon componentscomprising ring, normal and isoparafiin hydrocarbon components in asequence of hydrogenating conversion steps maintained under operatingconditions selected to obtain products rich in aromatics and LPGmaterial. More specifically, the invention is concerned with anarrangement and sequence of catalytic reactions designed to manipulatethe reaction of hydrocracking, dehydrogenation, isomerization anddehydrocyclization in an amount selected to improve upon the yields ofLPG products and relatively high octane aromatic components.

The present invention is concerned with contacting a relatively wideboiling range naphtha hydrocarbon material boiling in the range of Chydrocarbons up to about 380 or 400 F. under selective hydrocrackingconditions suitable for particularly removing the relatively low boilingC and C normal parafiins and not more than a minor amount of C parafiinsby a selective cracking thereof to LPG (propane and butane) products.The naphtha charge remaining after the selective removal particularly oflow boiling normal parafiin constituents and comprising C and higherboiling naphtha boiling range materials is subjected to reformingconditions in the presence of a platinum type reforming catalystmaintained under conditions selected to reestablish the presence ofnormal paraflins and thus a relationship approaching equilibrium betweennormal and branched compounds existing in the hydrocarbon chargeencountering the reforming reactions comprising dehydrogenation ofnaphthenes, isomerization of isomerizable hydrocarbons anddehydrocyclization of non-aromatic hydrocarbon constituents. Thus in thereforming operation of this invention, a relationship between branchedand normal paraflins is established in the normal paraffin deficienthydrocarbon material passed to reforming in combination with effectingthe production of relatively high octane components and particularlyrelative high octane aromatic and branched components. In this reformingoperation the conditions lead also to the production of relatively lowoctane branched and normal paraflin compounds which are available forconversion and production of additional LPG products. The reformingcatalyst may be relied upon to hydrocrack these low octane compoundsformed during the reforming operation by pushing the severity of thereforming operation but it is preferred that the reformate productcomprising any C and higher boiling normal paraffin constituents besubjected to a selective hydrocracking operation designed to convertparticularly the low boiling normal paraflins formed during theoperation. Thus the present invention includes the selective cracking oflow and high boiling normal paraflin components comprising the naphthaboiling material processed in the combination of catalytic contact stepscomprising this invention. It therefore includes reforming a naphthacharge depleted of the relatively low boiling normal paraffins butcontaining higher boiling normal parafiins generally 0, and higherboiling under reforming conditions particularly selected to establish arelationship approaching equilibrium in at least the normal and branchedchain hydrocarbons component along with performing the other reactionsof dehydrogenation and dehydrocyclization comprising catalyticreforming. This established relationship between normal and branchedchain hydrocarbon components brought about by the rearrangement ofbranched components provides additional normal paraffiu constituentssuitable for conversion to LPG material.

In the developments leading to the concepts of this invention, it hasbeen found that crystalline aluminosilicates of an average pore sizegenerally less than about 6 angstroms pore diameter but greater thanabout 4.5 angstroms, that is, about angstroms and comprising, forexample, erionite, are particularly selective for cracking of C normalparafiins to the substantial exclusion of cracking branched and ringconstituents. In addition, it has been found that a nickel erionitecrystalline aluminosilicate such as hereinafter described will have apreference for cracking normal C hydrocarbons to that of C C and higherboiling normal paraffin. On the other hand, a platinum type reformingcatalyst including bimetallic and non-bimetallic reforming catalysts andthose comprising platinum or palladium in combination with another GroupVIII metal component such as rhenium, iridium, ruthenium and osmiumpromoted with a halogen will indiscriminately effect hydrocrac'kingunder elevated temperature reforming conditions of the normal andbranched parafiin components comprising the hydrocarbon material in thereforming operation. Thus employing a platinum type reforming catalystunder controlled isomerizing and hydrocracking severity conditions maybe relied upon to produce LPG type products or products more easilyconverted to LPG products with a small pore nickel erionite selectivehydrocracking catalyst in another reaction zone or contact step. Thatis, hydrocracking reactions performed with platinum reforming catalystsare more usually rate controlled reactions wherein, for example, anormal C hydrocarbon will crack more easily than a C hydrocarbon or alower carbon number paraffin and thus a high severity reformingoperation would be required to crack, for example, a C paraflin.However, such a high severity non-selective hydrocracking operation withthe platinum reforming catalyst is undesirable since cracking ofbranched C and C hydrocarbons will be accomplished before cracking ofnormal hexane. This will result in cracking desired high octane branchedchain hydrocarbons. Furthermore, such an operation produces an undesiredmixture of light gases particularly comprising C and C hydrocarbonsrather than C and C hydrocarbons. On the other hand, using the smallpore selective hydrocracking catalyst described herein, cracking thelower boiling C and C paraflins in the naphtha charge and product ofreforming can be accomplished more effectively for the production of LPGproducts. Thus by maintaining a selective balance in rate control andequilibrium controlled hydrocracking reactions with the differentcatalysts described herein and particularly suitable for this purpose,an improved overall yield of LPG products can be obtained along with anaromatic rich product by the present invention.

Crystalline aluminosilicate conversion catalysts identified with theprior art which are not selective within the limits defined herein orthose particularly known as methane producers rather than producers ofpropane and butane are of little interest in pursuing the concepts ofthis invention. Furthermore, high methane producing crystallinealuminosilicate catalysts generally small pore crystalline zeolitespromoted with Zn, Cd and Hg or other hydrocracking catalyst compositionswhich non-selectively produce gaseous streams rich in methane are oflittle interest for practicing the concept of this invention unless theycan be controlled by operating conditions to exclude the undesirableproduction of light gaseous hydrocarbon constituents particularlymethane and ethane.

In the interest of convenience to a better understanding of the conceptsof the present invention the platinum type of reforming catalyst usedwill be referred to as catalyst A hereinafter, and the describedselective crystalline aluminosilicate hydrocrackin'g catalyst reliedupon particularly for the production of LPG gases will be referred tohereinafter as catalyst B.

The platinum type reforming catalyst, catalyst A, selected for use inthe sequence of process steps of this invention may be selected from anyone of a number of known prior art reforming catalysts suitable foraccomplishing the results desired. These catalysts include generally,for example, alumina as the carrier material for one or morehydrogenation-dehydrogenation components distributed thereon with thealumina being in either the eta, chi, gamma or mixed forms thereof. Thealumina carrier is promoted with, for example, one or more Group VIIImetal components either with or without an acidic promoter such assilica, boron or a 'halogen. The platinum type of reforming catalyst isintended to include platinum, palladium, osmium, iridium, ruthenium,rhenium and mixtures thereof deposited on an alumina containing carrieror support with the alumina components generally being in an amount upto about by weight. Other components such as magnesium, zirconium,thorium, vanadium and titanium may also be combined or distributed inthe alumina carrier. The platinum type catalyst may also include variousamounts of halogen such as chlorine or fluorine in amounts ranging fromabout 0.1% up to about 10%; usually not more than 5 or 6%. The platinumreforming catalysts described may be one of those described in the priorart as homogeneous mixtures of metal components, alloys, and metalhalide complexes thereof. A bimetal catalyst composition suitable forthe reforming operation of this invention may be platinum combined witheither rhenium, ruthenium, osmium or iridium and an alumina carrierpromoted with chlorine to provide desired acid activity.

The selective conversion catalyst or hydrocracking catalyst hereinreferred to as a type B catalyst is a porous solid particle materialhaving a majority of its pores of substantially uniform small dimensionwhich are large enough to allow uptake and egress of normal paraflinmolecules such as, for example, normal hexane and smaller carbon atoms,but too small to allow a similar uptake of either branched or ringcompounds such as, for example, methylpentane, cyclohexane or benzene.In addition, those hydrocarbons comprising C and longer chain normalparafiin hydrocarbons up to about C hydrocarbons encounter ditfusionlimitations which increase with length of chain and thus are slower tocrack when employing the small pore crystalline aluminosilicate catalystintended for use by this invention. Thus the selective hydrocrackingcatalytic material, type B, is a porous crystalline material wherein asubstantial majority of its pores are of an average uniform dimension ofabout 5 angstroms and in the range of from about 4.5 up to about 6.0angstrom units effective diameter. This is essentially a selectivecrystalline aluminosilicate of the erionite variety provided with inporeacid activity cracking sites and catalytically effectivebydrogenationdehydrogenation sites. In some cases thehydrogenation-dehydrogenation functions may be associated with the smallpore shape selective crystalline material but externally located to thepore and in some cases located both within and externally to the pore.On the other hand, it is contemplated providing the catalyticallyeffective hydrogenation-dehydrogenation sites restricted substantiallycompletely to within the pore. The hydrogenation-dehydrogenationcomponent provided during manufacture of the catalyst involves one ormore of the elements such as a transition metal. Preferably one or moreof the elements of nickel, cobalt, molybdenum, iron or of the platinumor palladium family are employed. One or more of the elements employedmay involve an element selected from a higher molecular weighttransition metal which have hydrogenation-dehydrogenation activity, suchas tungsten.

A crystalline aluminosilicate of desired porosity such as erionite maybe modified to produce useful catalysts for this invention by effectingthe introduction of one or more of the above identified transitionelements in such a way that the final quantity of the element may belocated in either the internal, external or mixed internalexternal porestructure of the crystalline aluminosilicate. Introduction of one ormore of such metallic elements or components may be achieved byprocesses allowing the metal to penetrate the existing or preformed poresolid and be fixed therein or by formation on the pore solid itself in acompositional environment which contains the desired metal component ina form suitable to be incorporated into the porous structure in theformation thereof, or in the course of its modification to a desiredpore structure.

It is preferred to impart the type B catalyst with certain limitedmagnitudes of acid catalytic activity. For example, when LPG product ispreferred over methane, the preferred acid activity will have an alphavalue in excess of 10. If the process employs the catalyst at atemperature of 900 F. or higher, a more preferred acidity level isbetween 5 and 300 alpha; for operations more nearly at 800 F., aboveabout 500 alpha; for operations near 700 F., above about 200 alpha. Avery practical method of assaying the alpha acidity of the type Bcatalyst is that of testing its n-hexane cracking activity underconditions of cracking, in the absence of hydrogen. Such a procedure isidentified in Journal of Catalysis, volume 4, No. 4, August 1965.

In reforming operations it is known that as the reforming severity isincreased to achieve higher and higher product octane number, the octanenumber increase is obtained primarily by way of paratiin aromatizationand 5 carbon ring aromatization. At the relative high severityconditions parafiin to aromatic dehydrocyclization reactions becomeimportant and are accompanied by progressive and non-selectiveelimination of remaining paraffins to light gaseous products thusincreasing octane number at the expense of substantial liquid volumeloss. However, by selectively controlling the reforming operationseverity the chemical reactions encountered therein are restricted tominimize the production of low octane and undesired gaseous component infavor of producing branched chain hydrocarbons in an aromatic enrichedproduct of relatively high octane rating. Accordingly, the method andcombination of process steps herein described provide significant andunusual benefits by adjusting the reaction mechanisms to implement andimprove the production of LPG products and high octane aromaticproducts.

The operating conditions employed in the proces combination of thisinvention and particularly that of the reforming operation with type Acatalyst are those conditions which promote dehydrogenation ofnaphthenes along with reactions associated with isomerization whichreestablish a relationship between normal paralfins to branchedparaffins and include operating temperatures selected from within therange of from about 800 F. to about 1000 F. and preferably from about850 F. up to about 980 F., liquid hourly space velocity in the range offrom about 0.1 to about 10, preferably from about 0.5 to about 5; apressure in the range of from about atmospheric up to about 600 p.s.i.g.and preferably from about 100 to about 400 p.s.i.g.; and a hydrogen tohydrocarbon ratio selected from within the range of from about 0.5 toabout 20 and preferably from about 1 to 10.

On the other hand, type B catalyst or the selective normal parafl'inconversion catalyst may be operated at conditions similar to reformingoperating conditions depending on the catalyst employed therein.However, it is important that the operating conditions be selected whichwill particularly promote the formation of LPG gaseous material from thehydrocarbon charge material brought in contact with type B catalyst.Therefore, catalyst type B Type B, catalyst example A naturalcrystalline aluminosilicate identified as erionite obtained from Nevadawas analyzed with the following results:

Weight percent Si0 68.4 A1 0 16.2 F6203 2.7 K 0 4.4 CaO 2.0 Na O 4.7 MgO1.3 Silica to alumina mol ratio 7.2

A sample of the above identified erionite was crushed to provide apowder. The powder was exchanged twice with 6 ml. of 5 M ammoniumchloride solution per gram (bone dry baiss) of the erionite powder for 4hours at F. with filtering after each exchange. Thereafter the exchangederionite is washed with 10 ml. of water per gram of erionite andfiltered. Then the erionite zeolite is exchanged with 4.4 ml. of 0.5 Mnickel acetate solution (adjusted to 6 pH with acetic acid) per gram ofthe zeolite for 4 hours at 210 F. and filtered. The nickel exchangedzeolite is then washed with 10 ml. of water per gram of zeolite andfiltered. The exchanged zeolite prepared as above identified is thendried for at least 16 hours or to a constant weight at a temperature inthe range of 225 to 250 F. The dried erionite zeolite promoted withnickel is then pelleted and crushed to a 10/14 mesh. The 10/14 meshrefers to passing through U.S. Standard Sieve No. 10 (Tyler equivalent 9mesh) and retained on U.S. Standard Sieve No. 14 (Tyler equivalent 12mesh).

SPECIFIC EMBODIMENTS In an effort to provide a better and more completeunderstanding of the method and process of this invention, the method ofimproving the yield of LPG gases comprising propane and butane findssupport in the following examples. Table 1 below identifies thecharacteristics of a light Arabian naphtha boiling in the range of Chydrocarbons up to about 340 F. which was processed in the combinationof steps of this invention comprising an initial selective hydrocrackingof normal parafiins boiling below about 0, hydrocarbons to LPG productsunder hydrogenating conditions employing a nickel-erionite catalystprepared as above identified before reforming of the remaininghydrocarbon material comprising C and higher boiling hydrocarbons with aplatinum under conditions to produce additional normal parafiins incombination with branched and aromatic constituents in a reformateproduct. The naphtha charge when containing undesired levels of sulfurand nitrogen may be subjected to an initial hydrofining or pretreatoperation wherein the sulfur and nitrogen constituents are reduced toless than 10 p.p.m. and more usually to about 2 p.p.m. by hydrogenationto products easily separated from a desired C or C naphtha charge.Hydrofining of the charge naphtha may be accomplished in the presence ofany one of a number of different hydrofining catalysts known andavailable in the prior art. Suitable hydrofining catalysts include themetals and/or sulfides of Group VIII and Group VI metals of the PeriodicTable employed alone or in combination with one another such as cobaltor nickel and molybdenum or tungsten. Such catalyst may be employedalone or in combination with a support or carrier material such asalumina, silica, zirconia, titania and clays or mixtures thereof.Generally the hydrofining catalyst is an amorphous base catalyst but itmay also contain a small amount of a crystalline aluminosilicate incombination with the amorphous carrier component. Suitable hydrofiningcatalysts include cobalt-molybdenum dispersed on alumina,nickel-tungsten sulfide alone or dispersed on a carrier or support suchas alumina or silica-alumina. In the hydrofining operation, temperature,pressure and space velocity conditions are selected from those wellknown in the prior art which will be effective in reducing the level ofnitrogen and sulfur in the charge to that suitable for initial contactwith the selective crystalline aluminosilicate conversion catalyst.

The selective crystalline aluminosilicate hydrocracking catalyst isfairly tolerant of nitrogen and sulfur compounds and thus will assistwith the removal of these contaminants during conversion of n-paraffincomponents in the naphtha charge. Thus the selective hydrocrackingcatalyst B may form a down-stream portion of the desulfurizing catalystbed. In a particular aspect it is important that the sulfur content ofthe naphtha brought in contact with the platinum reforming caalyst bereduced to an acceptable level of about ppm. and preferably to about 2p.p.m. for bimetal catalyst compositions such as platinum-rheniumdispersed on alumina. The amount of nitrogen in the naphtha reformingfeed should be reduced not to exceed about 2 p.p.m.

TABLE 1 Arabian light naphtha properties (C 340 F. cut) A naphtha chargesuch as identified in Table 1 Was passed sequentially through thecombination of catalyst contact steps comprising a selective crystallinealuminosilicate hydrocracking catalyst (SCI) for normal paraffinconversion to LPG, a platinum-aluminum reform-ing catalyst and then afinal contact with a selective crystalline aluminosilicate hydrocrackingcatalyst (8C2). Table 2 below identifies the operating conditionsemployed in one particular combination and provides the results obtainedwith the combination of conditions recited for improving productselectivity to LPG. The SCI and SCZ catalyst steps used the nickelerionite catalyst prepared as described above in combination with 0.6Wt. percent platinum dispersed on alumina and promoted with chlorine.Table 2 provides characteristics of the product obtained after each ofthe contacting steps as well as the cumulative yields obtained aftertraverse of the combination of processing steps. From these data it willbe observed that product selectivity to LPG product comprising C and Chydrocarbons was vastly improved by the combination of selectivehydrocracking before and i c r vit .72 2 :23 5 y 0 60 after reforming.It W111 also be observed that the aromatic R 41 rich high octane productof the combination process of M+ O 40 this invention has a much lowerbenzene content than a similar octane product of the processes compared.Thus Pona andlysls: P the combination of this invention is alsounexpectedly Paraflins eifective in reducing the concentration ofbenzene in a Naphthenes &5 high octane product suitable for use inpreparing motor Aromatics 9.5 fuels.

TABLE 2 Operating conditions S01 PtR S02 Temperature, F 800 900 800.Pressure, p si 2 500 500.-.. 500. Space velocity- 1 9 2.75. 2.1.

Total recycle ratio.. 4:0:

Catalyst Ni-erlonite. 0.6

10.0. pt. on alumina plus ch1orine- Ni-erlonite.

S01 SQ1+PtR l S1C1+PtR+S C2 PtR+SC1 PtR Wt Vol. Wt. Vol. Wt. Vol. Wt.Vol. Wt. Vol. Yields, percent on naphtha charge:

Hz. 0.6 1.2 0.1 0.8 1.1 0 4-0 2.4 5. 6 8.3 9. 1 9. 6 8x104 t73 g '5 g22. 0 30. 5 20. 6 27. 6 a 68. 1 62. 8 68. 7 63. 4 0 composition (Wt.percent on 05+ hycs):

N-C5. 2. 6 3. 9 1. 4 2. 2 6. 5 N-C. 0. 8 4. 5 0. 5 0. 5 2. 5 NC 2. 8 0.50.2 1.0 N-Cg. 0. 4 0. 1 0. 2 0. 1 N-Cn 0. 0 0.0 0.0 0.0 iso-Paraflins.28. 5 31. 4 31. 0 20. 1 Benzene. 4. 8 5. 3 5. 0 6. 3 Toluene 17. 1 18. 920. 0 21. 8 C gmrnafir'q 15. 4 17. 0 21. 7 23. 0 CH- m' 21. 3 23. 5 18.517. 8 CH- properties:

R+O 50. 8 94. 3 100 D+O 98. 3 97. 0 RVP. 4. 3 3. 9 5. 7 SPG'R 0. 7402 0.7787 0. 7940 0. 7869 1 Based on 05+ product from S01.

To further facilitate a more complete understanding of the contributionsof this invention, the data of Table 2 have been separated andrearranged to provide Tables 3 and 4 below. Table 3 below emphasizes theyield improvement in LPG material (C and C hydrocarbons) andparticularly that of propane obtained by the processing combination ofthis invention. Furthermore, differences in the product slate obtainedfrom the three dilferent identified operations are compared. Table 4, onthe other hand, particularly emphasizes the changes in the product slatefrom the different processing steps of the combination (SC1-l-PtR+SC2)particularly with respect to octane rating, C and C hydrocarbons yieldand the decrease yield of normal paraffins.

PtR PtR-l-SC2 SC1+PtR+SC2 Volume yield, percent of naphtha charge:

63. 4 62. 8 53. 7 Cs+C 27. 6 30. 5 45. 2 03-..- 13. 3 22.0 35. 3 i-C4 5.8 4. 9 3. 1 n-Cr 8. 5 3. 6 6. 8 Weight yield, percent:

n-Ca 1.7 0.3 0. 3 Aromatics 47. 2 44. 4 38. 1

TABLE 4 Weight yield percent of Naphtha S01 PtR SC2 naphtha chargecharge product product product n-C 6. 4 0. 6 2.8 0.3 i-Paraflins 44. 944. 9 18. 5 18.5 Aromatics. 11. 6 l1. 6 38. 1 38. 1 05+ (R+O) 41 50.894.3 100 Vol. percent Os+C 1 24. 7 37. 7 45. 2

It will be recognized by those skilled in the art that the combinationof processing steps comprising this invention and the product slateobtained therefrom can be varied by varying, for example, the reformingoperating conditions and/or the catalyst employed therein. For example,reforming catalysts of different composition are known to influence thevarious reforming reactions. Catalyst acidity may be employed toinfluence the various reactions of isomerization in the directiondesired. That is, acidic reforming catalyst may be relied upon toenhance isomen'zing reactions which change the balance between normaland branched parafiins and/or the cracking reactions encountereddepending upon the temperature and space velocity employed. A silicapromoted reforming catalyst may be selected to enhance dehydrocylizationreactions for example at temperatures less suitable for isomerizingreactions. Thus in the plurality of catalytic reaction zones comprisingthe reforming operation, a catalyst of very low acidity may be employedin the first reaction zone with subsequent reaction zones provided withcatalyst compositions of the same or diiferent acid activity to promotedesired reactions.

The processing combination of this invention contemplates the use of theselective crystalline aluminosilicate conversion catalyst (SCl) toeffect a part of the desulfurizing of the naphtha charged to theprocess. It also contempltes use of the crystalline selectivehydrocracking catalyst as a down stream portion of the hydrofiningcatalyst bed of a different composition such as CoMo on alumina or theselective hydrocracking catalyst (SCI) may be in admixture with thedesulfurizing catalyst. Under some circumstances it may be desirable tomaintain the hydrofining, catalyst and the selective nickel erioniteconversion catalyst in separate reactor beds with means between beds forremoving undesired gaseous constituent with or without means foraltering the temperature between catalyst beds as required. In any eventmeans are provided between the initial selective nickel erionitehydrocracking catalyst conversion step and the reforming step toseparate, for example, sulfur and nitrogen before passing the naphthacharge depleted of sulfur to a heating zone wherein it is heated eitheralone or in the presence of hydrogen to a temperature sufiicientlyelevated to effect primarily dehydrogenation of naphthenes therein uponcontact with the chlorine promoted platinum alumina reforming catalyst.The total product of the reforming operation may be passed in contactwith a selective crystalline aluminosilicate (CAS) conversion catalystsuch as nickel promoted erionite for the purpose of selectively crackingto LPG products only the n-parafiins found in the reformate product. Onthe other hand the reformate product may be first, separated to recoverC and h1gher boiling material from gaseous material lowei' boilmg than Chydrocarbons. Thereafter the C and higher boiling material andcomprising normal paraifin components therein formed during thereforming operation is passed in contact with the selective nickelerionite hydrocracking catalyst defined herein under desired temperatureand pressure hydrocracking conditions selected toachieve the furtherproduction of LPG products comprising C and C hydrocarbons as describedherein. The selective hydrocracking catalyst SC2 relied upon to convertnormal paraffins in the C reformate may be the same catalyst relied uponinitially to remove nparafiins and sulfur from the naphtha charge. Othercatalyst suitable for accomplishing this purpose may also be relied uponprovided the catalyst does not hydrogenate or otherwise destroyaromatics existing therein. Under some conditions a crystallinealuminosilicate hydrocracking catalyst of larger pore diameter than theparticular selective catalyst herein defined may be used provided itwill convert normal and some branched parafiin to form LPG productswithout destroying aromatics formed in the combmation.

The figure provided herewith presents one arrangement of a combinationof processing steps for practicing the present invention. In the figurea naphtha boiling range material such as used in the above examples andboiling from about C hydrocarbons up to about 340 F. is introduced tothe process by conduit 2. Hydrogen such as hydrogen rich gaseous productof reforming is introduced by conduit 4 for admixture with the naphthacharge being passed to a preheat furnace 6. In furnace 6 the mixture ispreheated to an elevated temperature in the range of 600 F. up to about800 F., or higher and sufiicient to effect desulfurization of thenaphtha upon contact with the desulfurizing catalyst or the combinationof catalysts provided in reactor 10 in this specific embodiment. Thepreheated naphtha boiling charge is passed by conduit 8 to reactor 10wherein is housed, in this specific embodi ment, an amorphous basedesulfurization catalyst 12 such as cobalt-molybdenum on alumina in anupper portion of the reactor and a selective crystalline aluminosilicate(CAS) hydrocracking catalyst (SCI or nickel erionite) 14 in the lowerportion of the reactor. When the naphtha charge contains only a smallamount of sulfur, then the sole fill of reactor 10, for example, may bethe selective catalyst (SCI) defined hereinbefore and having a pore sizeof about 5 A. and generally in the range of from about 4 to about 6angstroms since such material has been found to be a very acceptablematerial for desulfurizing the naphtha charge In reactor 10,desulfurization of the naphtha charge is accomplished along with theselective cracking of low boiling normal paraffins to the substantialexclusion of cracking higher boiling long chain normal parafiins,branched and ring compounds. In this selective cracking operation, atemperature of about 800 F. at a pressure of about 500 p.s.i.g. wasfound acceptable. The effluent of the catalyst reactions of reactor 10is then passed by conduit 16 to a separator 18. In separator 18 gaseousproducts comprising LPG material such as C and C hydrocarbons along withlower boiling hydrocarbons, hydrogen sulfide and ammonia as well asunconsumed hydrogen is removed from the upper portion thereof 'byconduit 20. This gaseous product is passed through equipment not shownto obtain a separation and recovery of LPG materials from the remaininggaseous product. Higher boiling hydrocarbon material and more usuallycomprising and higher boiling hydrocarbons are removed from separationstep 18 by conduit 22 for passage through a platinum catalyst reformingoperation. The platinum catalyst reforming operation depicted comprisesa plurality of sequentially arranged catalytic reactors pro vided withfurnace means for preheating the hydrocarbon charge passed to eachreactor to provide an inlet temperature of about 900 F. so thatprimarily dehydrogenation of naphthenes to form aromatics will beaccomplished in reactor 1 and 2 with the remaining reforming reactionsof isomerization, dehydrocyclization and hydrocracking being performedin reactors 2 and 3 under selected temperature reforming conditions. Thereforming reactors may be maintained at a pressure selected from withinthe range of 100 p.s.i.g. up to about 600 p.s.i.g. relying upontemperatures selected from within the range of from about 800 R, up toabout 1000 F. Thus in the specific combination of the processrepresented by the figure the hydrocarbon material in conduit 22 ispassed to furnace 24 in admixture with hydrogen containing gas admittedby conduit 23, wherein the mixture is preheated to an elevatedtemperature particularly suitable for effecting dehydrogenation ofnaphthenes in the mixture upon contact with a suitable platinumreforming catalyst in Pt. R1 or reactor 28. The effiuent of reactor 28is then passed by conduit 30 to furnace 32 wherein its temperature iselevated to that suitable for passage to PtRZ by conduit 34. In reactor36 dehydrogenation, isomerization and even some dehydrocyclizationreactions may occur. The eflluent from reactor 36 may be passed, ifdesired, by conduit 38 to furnace 40 for reheating thereof as requiredand before passage by conduit 42 to PtR3 or reactor 44. In reactor PtR3(44) reactions of dehydrocyclization and hydrocracking are promoted andcontrolled by the reaction conditions and catalyst composition employedtherein. Under some circumstances it may be desirable to replace all ora portion of the platinum reforming catalyst in reactor 44 with theshape selective conversion catalyst. In this arrangement the recovery ofproduct could be effected similarly to that disclosed in US. Pats.3,395,094 or 3,432,- 425. The reformate product, on the other hand, andcomprising the efiluent of reactor 44, as shown in the figure in thisembodiment, is then passed by conduit 46 to one or more separatorvessels represented by vessl 48. In separator 48, gaseous products ofreforming and comprising hydrogen are separated from higher boilingreformate material comprising C and higher boiling hydrocarbonsincluding aromatic enriched product of the process. The gaseous productof reforming boiling below C hydrocarbons is removed by conduit 50 andpassed to suitable recovery equipment not shown wherein hydrogen richgases are recovered from higher boiling hydrocarbons such as thoseforming LPG products. The higher boiling portion of the reformereffluent separated in separator 48 is removed by conduit 52 and senttofurnace 54 in admixture with hydrogen containing gas introduced byconduit 56. In furnace 54 the reformer effluent higher boiling than LPGmaterial is reheated to an elevated temperature before it is passed byconduit 58 to reactor 60 containing a selective conversion catalystrepresented as 5C2. In reactor 60 the reformer effluent boiling aboveLPG material and containing some formed normal paraffins during theplatinum catalyst reforming operation is subjected to a furtherselective cracking operation for the conversion of normal paraffincomponents to additional LPG material. The selective cracking of normalparafi'ins may be effected at temperatures below the reformingtemperatures relying upon pressures below, equal to or above thereforming pressure.

In the combination of processing steps comprising this invention anddiagrammatically depicted in the figure, a

considerable amount of equipment such as values, compressors, separatorequipment and recycle conduits are not shown for the purpose ofsimplifying the process depicted but are contemplated being used in suchas process combination. It should be understood furthermore thatrecycling of hydrogen rich gasses recovered from the gaseous product ofreforming to the reforming step and to either or both of the selectiveconversion steps is also contemplated. Other processing schemes forhandling the efiluent of the reforming operation and contacting portionsthereof with a selective conversion catalyst are discussed in US. Pat.3,432,425 and the use of such schemes are contemplated where appropriateby this invention. In the figure presented herewith, the efiluent of thenickel erionite selective hydrocracking operation is passed by conduit62 to separator 64. In separator 64, gaseous products comprising LPGmaterial such as propane and butane are separated and removed by conduit66 from a higher boiling aromatic enriched product removed by conduit68. The LPG material produced by the process combination of thisinvention is combined for further use as desired. The aromatic enrichedproduct formed by the combination and being of a high octane rating andrelatively low benzene content is thereafter used, for example, ingasoline blending operations.

Having thus provided a general discusion of the present invention anddiscussed specific examples in support thereof, it is to be understoodthat no undue restrictions are to be imposed by reason thereof except asprovided by the following claims.

I claim:

1. A method for upgrading naphtha boiling in the range of to 400 F. toproduce propane and a liquid product of high aromatic content whichcomprises,

(a) contacting a desulfurized naphtha and hydrogen with a selectivehydrocracking catalyst comprising acid erionite at a temperature in therange of 700 to 850 F. at a pressure in the range of 100 to 600 p.s.i.,

(b) separating C and lower boiling gasiform material from a higherboiling normally liquid naphtha material comprising C7 hydrocarbons,

(c) contacting the normally liquid naphtha material with a platinumcontaining reforming catalyst under reforming conditions selected toproduce a product comprising aromatics, branched and normal paraffinsand a normally gaseous stream comprising C and lower boilinghydrocarbons,

(d) separating a normally liquid reformate product stream comprising Cand higher boiling reformate product from lower boiling gasiforrnmaterial,

(e) contacting the normally liquid reformate product stream with ahydrocracking catalyst comprising acid erionite under conditionsselective for converting nparafiins to LPG product gas and (f)recovering from each of said selective hydrocracking a product rich inpropane and an aromatic rich product from said second selectivehydrocracking operation.

2. The method of claim 1 wherein the selective hydrocracking isrestricted primarily to C normal paraffins.

3. The method of claim 1 wherein the selective hydrocracking of normalparafiins is controlled by pressure, space velocity and use of acrystalline zeolite of about 5 angstrom average pore size provided within pore hydrogenation-dehydrogenation activity.

4. The method of claim 3 wherein the hydrocracking catalyst comprisesacid nickel erionite.

5. The method of claim 1 wherein the selective hydrocracking of thenaphthas charge is accomplished in a downstream portion of a naphthadesulfurizing zone and the selective hydrocracking of liquid reformateproduct is accomplished in a downstream portion of the last reformingzone.

6. The method of claim 1 wherein the selective hydrocracking of thenaphtha charge occurs at a temperature in the range of 700 to 850 F. ata pressure within the range of 100 to 600 p.s.i. and the selectivehydrocracking of the liquid reformate occurs at a temperature within therange of 800 to 1000 F. at a pressure within the range of 100 to 600p.s.i.

7. The method of claim 1 wherein the reforming operation is accomplishedat a higher temperature than the selective hydrocracking steps.

8. The method of claim 1 wherein the selective hydrocracking steps areaccomplished in separate reaction zones.

References Cited UNITED STATES PATENTS 0 HERBERT LEVINE, PrimaryExaminer 208-65, DIG. 2

US. Cl. X.R.

